A new look to azimuthal modulations and extraction of generalized parton distributions*

Azimuthal modulations are crucial in the phenomenological extraction and separation of various generalized parton distributions (GPDs). Traditionally, GPDs could be extracted from angular modulations of the deeply virtual Compton scattering (DVCS) in the Breit frame. However, the Bethe-Heitler subprocess (BH) interferes with the DVCS and contaminates the azimuthal modulations from DVCS, making it challenging to extract GPDs cleanly. We provide a new formalism and choice of frame to describe the azimuthal distributions, and demonstrate that they are more suitable for experimental analysis to separate contributions to a physical cross section from GPD sensitive (such as DVCS) and insensitive (e.g., BH) subprocesses in a consistent and uniform way.